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Modelisation and Simulation of turbulent flames enriched with hydrogen

MEGEP (Mécanique, Energétique, Génie civil & Procédés)

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The energy transition requires a drastic reduction in greenhouse gas emissions, particularly in the transport and power generation sectors.  
Hydrogen, used as an energy carrier or fuel, is emerging as a promising solution to decarbonize combustion.  
However, its unique physical properties — high diffusivity, low molecular mass, and strong chemical reactivity — profoundly modify mixing, transport, and combustion mechanisms.  
As a result, differential diffusion and molecular transport effects become critical for the accurate numerical description of flames, whether laminar or turbulent.  

In this work, a detailed \textit{mixture-averaged} transport model was implemented, validated, and assessed in the compressible LES solver AVBP, in comparison with the historical simplified model based on constant Schmidt and Prandtl numbers.  
The validation first focused on one-dimensional premixed flames, where AVBP results showed excellent agreement with Cantera predictions for temperature, species profiles, and laminar flame speeds.  

The study was then extended to three-dimensional configurations.  
The laminar LAMIRADAS flames provided the first 3D validation of the model for methane–air and methane–hydrogen–air mixtures.  
The results showed that, in such regimes, differences between the detailed and simplified models remain marginal: the flame position, structure, and dynamics are nearly identical, even in the presence of hydrogen enrichment.  

The model was next applied to a turbulent diffusion flame of hydrogen–air (HYLON).  
In this configuration, discrepancies between the two models were localized in the central recirculation zone, where molecular diffusion and heat transfer dominate.  
The simplified model overpredicts thermal conductivity, viscosity, and, most notably, radical diffusivities, leading to higher local temperatures and an overestimation of NO formation compared with the detailed formulation.  
These results, published, highlighted the importance of detailed transport modeling for accurately predicting pollutant formation in turbulent hydrogen–air diffusion flames.  

Finally, the MIRADAS configuration — a turbulent partially premixed methane–hydrogen–air flame — confirmed the relevance of the new transport model in a more complex regime combining premixed and diffusive combustion.  
While global differences between models remain small, significant local deviations appear in hydrogen-rich regions, where differential diffusion strongly influences flame stabilization and local dynamics.  

In conclusion, this thesis provides AVBP with a complete, accurate, and numerically efficient molecular transport model.  
The mixture-averaged formulation now offers a robust framework for LES of reactive multicomponent flows and opens new perspectives for studying hydrogen–air and hydrogen–hydrocarbon–air combustion systems.

Jury

Aymeric VIÉ	Professeur Centrale Supelec – EM2C	Reviewer
Pascale DOMINGO	Directrice de recherche CNRS – CORIA	Reviewer
Thierry SCHULLER	Professeur – Université de Toulouse	Examiner
Cédric MEHL	Ingénieur de recherche – IFPEN	Examiner
Jean-Christophe JOUHAUD	Chercheur – CERFACS	Thesis supervisor
Eleonore RIBER	Chercheur – CERFACS	Invited
Bénédicte CUENOT	Ingénieur Expert Combustion – Safran AE	Invited